3400 build Plans Finally Complete

[Superdave]

What can i do just using stock pistons and acheive very close to 10:1?

Have .020" shaved off the tops of the pistons and run the thinner .040" RWD gaskets...

[sprucegagt]

you would end up with a 11.56.1CR using the camaro pistons and the 3500 heads

I thought it was the DOHC pistons w/ 3500 heads that got you 11.5:1.

[SappySE107]

Nope, thats roughly 12.4:1 depending on the overbore. This was with .040 over.

[geldartb]

I thought it was the DOHC pistons w/ 3500 heads that got you 11.5:1.

the only things i changed were the CC size of the 3500 heads which i found on here and the dish size of the pistons and the deck clearance, everything else is the same since you wouldnt be changing that.

[sprucegagt]

Ok. Who has a link to the compression ratio calculator?

[geldartb]

i had to do a little searching before to find it

http://wiki.60degreev6.com/index.php?title=Compression_Ratio_Calculator

[sprucegagt]

What's the "Piston Deck Clearance" dimension? I don't understand were the 0.0095" spec that you used is coming from. I thought 3400 pistons came proud of the block by 0.020". Given how small the spec is it makes me think it's the piston to bore clearance. Am I right?

[bszopi]

The piston deck clearance should be the distance it comes out of the block. The 0.0095" spec is a value that I think I built into the database prior to the measured value of 0.020". I'm pretty sure I came up with that number by looking through old posts and calculating the value given other piston values. I don't know, its been so long since I created the original program and database entries.

[sprucegagt]

Well if that is the piston to deck clearance, then the actual value you would use is -.020. If so then what piston could you use to get 11.5:1 compression without getting custom pistons. I ask because iron head 3.4 pistons get you 12.6:1 and DOHC get 13.4:1 and they aren't exactly streetable w/ pump gas.

[bszopi]

Right. Look at the 3100 default values, and you will see that is what it has. If you use all the same values for volumes as the 3100 (piston dome and combustion chamber), plus the -0.020" value, then you come up with a stock CR for the 3400 of 9.93:1. If you change it to -0.015" (which I think I saw some mention the other day somewhere), it comes out to 9.81:1.

In order to come up with an exact value, you should use actual measured values from your specific components. Depending on porting work and such, CC volume will definately be different.

[ForcedFirebird]

3.4 pistons do not stick out of the block, hence the .040" gaskets on the iron heads.

3500 heads and 3.4 Camaro pistons make 11.5:1 with 3500 gaskets, 3400 gaskets gives 11.75:1 and 3.4 gaskets give 12.33:1. The 3x00 gaskets actually leave a little too much clearance between the heads and pistons, .040" is supposed to be ideal. SI valves will raise it a bit more, too.

Hey Ben, did you use the cam do bring down the CR? Would you mind sharing details of the tune if you used OBD1? My new combo for my car isn't going to be too far off from the one you built.

EDIT: What is the DOHC piston to deck clearance?

[sprucegagt]

In order to come up with an exact value, you should use actual measured values from your specific components. Depending on porting work and such, CC volume will definately be different.

I definitely agree. I'm just looking to get a good estimate. Finding out I have 12.4:1 during assembly when I'm expecting 11.5:1 isn't a good thing.

3.4 pistons do not stick out of the block, hence the .040" gaskets on the iron heads.

3500 heads and 3.4 Camaro pistons make 11.5:1 with 3500 gaskets, 3400 gaskets gives 11.75:1 and 3.4 gaskets give 12.33:1. The 3x00 gaskets actually leave a little too much clearance between the heads and pistons, .040" is supposed to be ideal. SI valves will raise it a bit more, too.

Hey Ben, did you use the cam do bring down the CR? Would you mind sharing details of the tune if you used OBD1? My new combo for my car isn't going to be too far off from the one you built.

EDIT: What is the DOHC piston to deck clearance?

What head gasket bores are you using for the 3400 and 3500 gaskets because I'm not getting the same values as you.

[ForcedFirebird]

3500 gaskets have a 3.80" bore and the 3400 gaskets have 3.75", both are .060" compressed height. The 3.4 gaskets also have a 3.75" bore.

Remember the 3.4 pistons have a .0095" deck clearance.

EDIT: Sorry, I fogot to use the 3400 gasket ht, 3400 gaskets and 3.4 pistons make 11.56:1

Are you using the 3500's 32.4cc chambers?

[sprucegagt]

Now that matches what I got.

I'm using 3500 heads but they have been milled .010, so chamber volume has dropped a little. How much I don't know.

[bszopi]

Now that matches what I got.

I'm using 3500 heads but they have been milled .010, so chamber volume has dropped a little. How much I don't know.

Time to break out the burrette or syringe! Oh yeah, and I've added the CR calculator to the new site, so there is now a link to it on the left side menus. I've also got the specifications back up as well.